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Throttle response? Not MAF

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by SteveX, Nov 26, 2012.

  1. SteveX

    SteveX Senior Member

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    Hi Guys,

    Popped a new Bosch MAF in the car and same problem! I guess we can rule that one out.

    I've identified now that the problem occurs even when not at speed, so if I squeeze the throttle on it seems to be fine, if I dump the accelerator to the floor to hit kickdown at any speed the car bugs out.

    All gears remain, however the throttle response is nearly non existent!

    Pressing the pedal fully again achieves nothing, the car doesn't accelerate, gently squeezing it gets to perhaps 50% of the pedal movement then starts to pick up, even in neutral.

    I've got it booked in to get the codes read, but could the kick down switch cause the throttle to behave this way if faulty? Similarly, if the throttle is stamped down quickly would a faulty pedal position sensor bug out?

    A quick stop and start solves the issue. If I keep the throttle pressed to the floor at low speed it will accelerate and pick up beyond 3k rpm, however I suspect the issue I had when at speed is that more throttle is required and there just isn't any there, so the car is sluggish, hardly pulls and lingers around 3k.


    Cheers,
     
    Last edited: Nov 26, 2012
  2. rpe2

    rpe2 Senior Member

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    Your Mercedes:
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    What car do you have?
     
  3. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    You posted a similar thread last week to which I replied, get the codes read before replacing parts etc. No ideas or suggestions can be put forward with out having some data to go on first. Replacing parts is not the most cost effective way of diagnosing a fault!
     
  4. Miffy

    Miffy Senior Member

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    I had something similar on my clk, fault codes said it was a faulty TPS. Changed it and the problem has not come back. But as Steve says, don't be guessing, get the fault codes read.
     
  5. star

    star Forum Supporter Authorised Forum Supporter

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    +1.
     
  6. OP
    SteveX

    SteveX Senior Member

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    I'm afraid It isn't the most cost effective way when it turns out that your local BMW / Mercedes indi want's to rip you off and you do not trust them....

    I found out today it's the same dodgy place I took my M3 to for a slight blow on the manifold at the bottom of the down-pipe, to which he said it needed two new manifolds at £1400, new catalytic convertors at £1200, and a whole bunch of other stuff that I knew was BS.

    Ended up taking it to munich Legends and they repaired a common 'flexi' joint issue by welding a new one in, everything else was fine. Cost? £120.00

    Was a good few hours drive and a fair bit of fuel though, but it wasn't dangerous to drive.

    I took a punt at the MAF as it seemed likely, but at least now I know it isn't so I'm just going to resell it.

    I appreciate there are some reputable Indi's around, but it's finding one that isn't hours away just to pull some codes (I don't want to drive the car too far when it isn't running right).
     
    Last edited: Nov 26, 2012
  7. OP
    SteveX

    SteveX Senior Member

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    Thanks, yes I'm thinking it points to something similar.

    Thankfully I got the MAF at cost anyway through a friend in the trade, so I'm happy that it has ruled that problem out - I'll just sell it on.

    I can replicate the issue when starting the car in neutral, I've found out it has nothing to do with RPM, travel speed or gear box. If I quickly stamp my foot to the floor in neutral something loses the signal or stops responding.

    It's not the kickdown switch either, as I manually clicked it, then tried revving and everything was fine.

    The throttle cable moves perfectly from the pedal to the Pedal Value Sensor, the sensor however looks like it has been tampered with before my ownership.

    It's not the TB sticking as the revs drop fine, it's the signal or response between the Pedal Value Sensor and the throttle body, or potentially the throttle body motor.

    I'm currently trying to source some kit to pull the codes myself, but it's the pre OBDII set up so will cost a bit. I don't know of any good Indi's in this area unfortunately - the one I was going to take it to I found out was the same terrible place I used a while ago and they had just changed their name - shall not be going there!

    Richard, it's a CLK 320 W208 :)

    Cheers!
     
    Last edited: Nov 26, 2012
  8. NW_Merc

    NW_Merc Banned

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    Where are you in the country?
     
  9. OP
    SteveX

    SteveX Senior Member

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    Hi,

    I'm in Wiltshire :)


    Cheers,
     
  10. OP
    SteveX

    SteveX Senior Member

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    Ok, so the saga continues!

    I've ordered a Carsoft 7.4 and software today to help with reading the codes etc.

    Also did a voltage test on the Pedal Value Sensor, the result was that before and after the fault, the correct voltage on both circuits of 0 - 2.5v (Aprx) and 0 - 4.75 occured. The 5v constant from the ECU was also fine.

    Whether however the fault occurs during a very quick application of WOT on the sensor which confuses the ECU or not I do not know, but in either case, I would imagine the ECU should adapt based on the correct voltage / signal coming from the sensor.

    I have noticed when turning the ignition on however but not starting the car that there is a constant buzzing from the area near the throttle body, moving the Pedal Sensor results in the motor moving, and being heard, however it does sound a bit mechanical.

    I'm guessing that it's now either an issue with the ECU or the throttle body itself / motor. Fingers crossed it's just the throttle body motor!


    Cheers,
     
  11. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Where in Wilts are you? You are less than an hour from me down the A303, why not pop down and I will give you a hand as I have STAR! You need to check live data to see what is going on, not just fault codes! Im not sure if the carsoft product will help you there.
     
  12. OP
    SteveX

    SteveX Senior Member

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    Cheers Steve,

    I'm in Swindon, Google maps seems to think your 80 miles or nearly 2 hrs away from me though :( although that is the motor way.

    I'm not using the car at the moment as I'd ideally like to get this fault sorted before shifting / using it.

    If I don't get any success after spending the weekend on it, or with the carsoft (if it turns up ;)) it's certainly going to be time to let the pros look at it ;)


    Cheers,
     
    Last edited: Nov 29, 2012
  13. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Thought you might be more Devizes/Melksham/Marlborough way. Although I bet I could get here quicker than 2 hours from Swindon!!!
     
  14. bigtwin

    bigtwin Banned

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    Bristol 2 hrs from Swindon? - 40 miles. Only if you pick the wrong traffic scenario. I can be in Bristol town centre from Guildford in 2 hours near as dammit without having to smash the 80 barrier. Swindon is usually nearly an hour.
     
  15. OP
    SteveX

    SteveX Senior Member

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    I could as well, just depended how many times I had to stop and start the car lol :)
     
  16. OP
    SteveX

    SteveX Senior Member

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    No Swindon to Matlock :)
     
  17. Alex Crow

    Alex Crow Senior Member

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    You have added 2 and 2, and come to an answer that is not 4.

    I will take a guess, a stab - fuel pressure regulation, possibly a pattern fuel filter has been fitted.
    This is a guess, based on my years of experience working on these cars, but I will always test first, and replace that which is at fault when proven to be so.

    The buzzing of the throttle body is correct, and I am sure the ECU and throttle position sensor do not deserve to be under suspicion, based on the information you have presented.

    I have never yet had to replce a throttle body on a 112, can't actually remember the last one that I changed in fact, so it is some years...
     
  18. OP
    SteveX

    SteveX Senior Member

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    Thanks Alex.

    Appreciate everyone's input, if you guys were a bit closer I would nip it over.

    Not that I want to take business away from you but if anyone can recommend a place close it would be good :)
     
  19. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    I dont think we have an Indie who posts on here from the Swindon area, people who visit here normally visit me, Cole at MBS or Ian at Star in Caversham.
     
  20. OP
    SteveX

    SteveX Senior Member

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    Thanks guys, as it happens a voicemail popped into my mail box this morning, found a chap who works for merc and so had all the genuine kit, he read the codes for me on the side today just round the corner from me.

    £60.00 so not too bad, he cleared all codes, reloaded all factory settings and we tested, fault ocured, re-checked and there was only one fault - it was....(drum roll)........

    Logged as the Pedal Value Sensor!

    Bizarre given the output of the sensor seems spot on - just goes to show checking with a volt meter isn't a great way to diagnose sensors (lesson learnt!).

    Going to order one in from ECP today, should be here in a couple of days and with discount only £70.00.

    Done a shed load more to the car the past couple of days too, so just this and get a new locker then I can move on!


    Cheers all!
     

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